The present invention relates to an apparatus for use in converting solid thermoplastic material to molten thermoplastic material to facilitate application of the thermoplastic material to an article.
A known apparatus for use in converting solid thermoplastic material to molten thermoplastic material, such as hot melt adhesives, includes a tank which is enclosed by a housing and receives the solid thermoplastic material. The solid thermoplastic material is melted by heaters connected with the tank. The molten thermoplastic material is conducted from the tank to dispensing guns which apply the molten thermoplastic material to articles. Some known designs for thermoplastic material melting apparatus are disclosed in U.S. Pat. Nos. 4,456,151; 4,485,942; and 4,883,200.
Maintaining the apparatus clean and free of bacteria is extremely important when the apparatus is to be used in association with the application of hot thermoplastic material to containers for food. Cracks and/or crevices in the housing may provide a place where bacteria may accumulate. To eliminate this accumulation of bacteria, it is common to wash the unit with cleaning agents. For example, it is common to literally hose down the unit. However, it is not uncommon in the dispensing or melting of hot melt adhesives to experience temperatures in the range from about 71.degree. C. (160.degree. F.) to about 232.degree. C. (450.degree. F.). It is therefore important to keep the cleaning solution from entering the tank during a wash down.